The Dremel tool with a router attachment is the way to go. Just make some thin plywood templates and place them where you need the cutout, set the depth and get after it. You can melt the passages in the foam wing with a heated piece of 1/4" piano wire. If you route the channels for the servo wires you will have to cap them off with something.

Forgot to add, when you do this wear a respirator, eye protection, and keep a vacuum handy for frequent clean up's, as this really makes a mess.

Vince